Significance of the Protein Level in Synthetic Diets

Summary

It has been reported by McIntire et at. that a diet containing 18% purified casein and 6 pure B factors does not support optimal growth in male rats, and that the missing factor is present in liver extract. Evidence is presented to show that the factor, whatever it is, may not easily be found in the usual concentrated sources of B complex, but rather that it is associated, whether as an impurity or an essential amino acid, with protein of good quality.